Bad index macro use fix

[wgropp]

Problem

In two places, an indexing macro is used incorrectly, leading to incorrect text. Specifically, p 483 and p 495, where the incorrect indexing macro use (causes "MPI process initialization@MPI process initialization" in the text.

Proposal

Fix the macro use.

Changes to the Text

Corrects the text as intended

Impact on Implementations

None

Impact on Users

Improves the quality of the document

References and Pull Requests

See PR mpi-forum/mpi-standard/pull/1114